We seek a shared BIAcore 3000 surface plasmon resonance biosensor, to be used for 3 immediate applications; 1 - To demonstrate direct physical interaction between molecules and to distinguish the relative strength of physical interactions between different candidates 2- To map the amino acids and areas of contact that dictate interaction with binding partners and quantitate the relative affinities of modified proteins or peptides with their binding partners. 3- To test the feasibility of identifying interacting molecules in complex mixtures Understanding the molecular networks that dictate cell behavior proceeds through several steps. First, identifying all the elements that affect the function of a process or pathway; second, identifying which elements interact physically; third, identifying the relative strength of the interaction between one molecule and other potential binding partners; and finally, determining how altered conditions or environments (e.g. pH, concentration, phosphorylation etc) affect the nature of molecular interactions. Measurements of molecular interaction are increasingly important in many areas of investigation. Of particular importance to our group is the need to test genetic interaction data by direct measurements of physical interaction. Although several approaches can be used to monitor physical interaction (e.g. yeast two-hybrid, co-immunoprecipitation etc), those methods are all technically challenging. Biosensor technology is fast, sensitive, quantitative and technically much easier than these other approaches. It is also generally applicable in that it does not rely on specific properties of the interacting molecules other than their physical interaction. In addition, once interactions are detected using biosensor technology, quantitative measurements of kinetic rate constants and equilibrium association constants can be made using the same immobilized receptor and ligand preparations, thus saving considerable time and effort. The projects listed here (as well as others) would reap huge benefit from rapid measurements of molecular interactions.